Field of the Disclosure
The present disclosure relates to an organic electroluminescent device (OELD), and particularly, an organic electroluminescent device configured such that when a pixel having a bright spot defect or dark spot defect is identified, the defective pixel can be operated identically with a neighboring pixel, and a repairing method thereof.
Discussion of the Prior Art
An organic electroluminescent device, which is a flat panel display, has properties of high brightness and low driving voltage. Further, because the organic electroluminescent device is a self-luminous type device, it has advantages of high contrast ratio, thin profile, fast response time of about several microseconds, no limit to viewing angle, stability at low temperature, and simple manufacturing and design of driving circuitry because the device operates at a low voltage of DC 5V to 15V.
Accordingly, the organic electroluminescent device having the above advantages is recently used for various electronic IT (information technology) devices such as TVs, monitors, and mobile phones.
The organic electroluminescent device includes an array element and an organic light emitting diode (OLED). The array element includes a switching thin film transistor (TFT) and at least one driving TFT connected to the organic light emitting diode. The organic light emitting diode includes a first electrode connected to the driving TFT, an organic light emitting layer, and a second electrode.
The organic electroluminescent device may display full color images using organic light emitting materials emitting red, green, and blue, respectively. Alternatively, the organic electroluminescent device may display full color images using organic light emitting materials all emitting white with red, green, and blue color filter patterns in respective pixel regions.
However, there is a defect in that a property of the driving TFT is degraded or an internal short circuit of the TFT occurs during manufacturing signal lines, switching TFTs, and driving TFTs, and thus the TFT does not operate normally.
When the TFT is not operating normally, current does not flow to the organic light emitting diode, and a pixel having the TFT becomes a dark spot. When there is a short-circuit between source and drain electrodes of the driving TFT, a driving voltage is directly applied to the drain electrode regardless of the driving TFT being turned on/off, and thus a pixel having the TFT is in on state at all times and becomes a bright spot.
In the case of the dark spot, because it is impossible to repair the dark-spot pixel, this pixel remains as it is. In the case of the bright spot, disconnection between the driving TFT and the first electrode and disconnection between the driving TFT and the switching TFT are made by a laser cutting method. Further, the first and second electrodes of the organic light emitting diode are connected by a welding method, whereby the pixel becomes a dark spot.
In this regard, the bright spot is relatively more visible to a user, and thus even though there may not be many bright spots occur in the display device, the display device may be disqualified and does not become a final product. On the other hand, dark spots are relatively less visible by a user. Particularly, about 10 to 20 dark spots in the display device are hardly visible by a user. Accordingly, in the case that the bright spot exists, the process of changing the bright spot into dark spot is conducted.
Recently, display devices of high resolution such as full HD (high definition) or UHD (ultra-high definition) are available, and users are growing more and more interested in display quality. Accordingly, a product having 5 or less spot defects is required.
However, there may have been no methods to repair the dark spot due to the nature of the display device. Further, because hundreds of thousands of pixels exist[s] in a display device, failure cost to manufacture the display device having all the pixels non-defective increases a lot, and thus production cost increases.